I do this every day. My solution is to simply Remote Desktop into the other computers. If all the computers are plugged into the same wired ethernet subnet, the performance of Remote Desktop is quite snappy these days. Even wifi isn't bad, but I start to feel a bit of lag on wifi, so I prefer wired. I wouldn't play games or do video/audio editing that way, but for basic office work, wired RDP is totally acceptable.

There are advantages to doing it this way:
- Your "main" operating system can be anything you want (mac, Linux, Windows) and it can be your personal machine if you like.
- You can arrange the remote desktops however you want on your main system. They can be run fullscreen or in a window (any size window you like) and can be closed/opened and moved around at will.
- You can copy and paste text, and FILES, to and from the remote desktops! This is massively useful!
- If you configure the other laptops power management features, so that the "Lid Close Action" is set to "Do Nothing", then you can just leave the other computers in a stack, off to the side, lids closed and running. Power them on or off as needed, lids can stay closed. Do whatever you need for ventilation for them.

I have two LCD monitors, and to the left of the monitors, is my stack of laptops, with my main laptop (macbook) on the top of the stack. I have the macbook lid open, and the other laptop lids are closed, underneath the macbook. So I have three screens total, and I can choose to RDP into the other laptops at any time and move their windows around on any of the three screens.

On the rare occasion that I need to access one of the other laptops directly, rather than through RDP (example: Changing a BIOS setting), then I can just move the mac aside and open the lid of the other laptop and go for it. I also have an additional fancy setup which is totally optional which I rarely use, it's basically a poor man's KVM: The other laptops are plugged into USB docks with HDMI outputs, and those outputs can be temporarily routed to my LCD monitors. And since my monitors have two inputs (each monitor has a DVI and an HDMI input), the extra laptop which I would be most likely to use with those monitors, already has its outputs plugged into DVI cable adapters and they're going into the DVI inputs on my monitors. So on the rare occasion that I want that extra laptop to be multimonitor direct-connnect, I don't even have to futz with cables, I just press the input-select button on the monitors.

The only possible wrinkle is that maybe some of his extra machines might have some kind of lockdown preventing RDP connections. However, if he has full keyboard access to the machines (an administrator login) then he should be able to make the necessary configuration changes to allow RDP access. Maybe some hoops to jump through, there.